Many electronic devices can be powered by more than one power source. For example, mobile devices, like notebook computers, can usually be plugged into an AC electric outlet or operated on battery power. These kinds of electronic devices usually include some sort of power system to select from among the available power sources.
FIG. 1 illustrates one example of a typical power system that may be found in any number of electronic devices, such as a notebook computer. An external AC power source 115 is optional. That is, the device may or may not be plugged into an electric outlet at any particular time. An AC/DC converter 110 can convert the AC power (if it is available) to an unregulated, or loosely regulated, DC voltage 180. The DC voltage 180 is unregulated, or loosely regulated, in that converter 110 may not actively control the voltage. Instead, converter 110 may be a passive filter or transformer.
Any number of devices can be used for converter 110. The most familiar kinds of AC/DC converters are rather large blocks that are part of a power cord or power plug. A typical unregulated voltage for a notebook computer is about 20 volts.
The power system also includes two additional power sources, battery pack 140 and battery pack 150. Battery packs 140 and 150 each provide a battery voltage 190. Any number of battery pack designs can be used. A typical battery pack for a notebook computer may include six battery cells coupled in two parallel groups of three cells in series. The safe voltage range for an individual lithium cell is often about 3 to 4.2 volts. That is, a fully charged lithium battery cell will typically provide about 4.2 volts, and the voltage will fall off to about 3 volts as the battery discharges. With three lithium cells in series, a battery pack will often provide a safe voltage range of about 9 to 12.6 volts. Other power systems may include more battery packs or just one battery pack. Other typical battery packs may include different combinations or configurations of battery cells. And, other battery cell chemistries can be used and can provide different voltage ranges.
Source selector 160 selects from among the available power sources based on switch control signal 107. That is, either the unregulated voltage 180 or the battery voltage 190 from one or both of the battery packs can be coupled to the power rail 170 at any particular time. In which case, for a typical notebook computer, the rail voltage 195 can range from about 9 to 20 volts. Power rail 170 can supply power to a wide variety of components and circuits within the electronic device (not shown).
The illustrated example also includes a battery charger 120 and a charging selector 130. Charger 120 can generate a battery voltage 190 from the unregulated voltage 180 (if available). Charging selector 130 can supply the battery voltage 190 to recharge either battery pack 140 or battery pack 150 based on switch control signal 105.
The switch control signals 105 and 107 can come from any number of sources. For example, in a notebook computer, an operating system may generate the control signals. Whatever the source is for the control signals, it may detect when AC power is available, as well as monitor the power levels of the battery packs, to generate the appropriate control signals. Any number of approaches can be used to select which battery to recharge and which power source to use at any given time.